In filling machines for liquid food packages, such as sold by Tetra Pak® under the name Tetra Pak A1, a web of packaging material is sterilized, and is subsequently formed into a tube. This tube is filled with liquid food continually, and the tube of packaging material is transversally sealed and cut such that separate packages with liquid food are formed. The liquid food is generally filled inside the tube of packaging material up to a certain height, such that a certain pressure is created during the forming and sealing of the packages. Normally, the pillar of liquid food is enough for having good package forming, but in certain instances an additional over-pressure is required. This is normally provided by connecting a tube system of pressurised sterile air to the filling pipe, providing an over-pressure inside the tube of packaging material, acting on the pillar of liquid food and being maintained by a tube seal, arranged inside the tube of packaging material and sealing against the internal pipes. However, the pressure above the liquid pillar is difficult to measure, and may fluctuate during production, for various reasons.
It is hence an object of the present invention to mitigate this drawback. In a first aspect, the invention provides a system for accurately monitoring the pressure inside the tube of packaging material by utilizing a method according to claim 1.
All features described in connection with any aspect of the invention can be used with any other aspect of the invention.